After my original post, I did email LCC asking for further information and received an initial acknowledgment, but no further reply.I've just come across some more information on this thanks to Geocaching.com and a recent 'earthcache' (information about geological features)

"Sadly, this Geological Garden no longer exists, and even local people are hard pushed to tell you where exactly it stood, or how long ago it was removed. In fact, it stood on the banks of the river near where the bowling green is now, and was the brainchild of Henry Cherry Versey, a local and celebrated geologist born in 1894 who died in 1990. Samples of rock included some rare granites and marbles, as well as more everyday examples, set out on a foot map of the British Isles, with plaques telling visitors about the location and qualities of the rocks displayed. Some locals remember it as a 'graveyard' due to the way the slabs of stone stood, and when it fell into disrepair, and became a little-visited corner of the grounds, it was eventually removed in around 2004. It stands in history now as a much misunderstood and misinterpreted idea, but lives on today with this EarthCache. No matter what happened to his garden, I suspect Mr Versey would approve of EarthCaches."

Hi Croggy1 . Thanks for that interesting information about the Geological Garden.

I've just had a look at the Old Maps UK website and this (hopefully!) is a link to its 1969-1973 1:1,250 map that shows the location of the Geological Garden:- https://www.old-maps.co.uk/#/Map/426045/436252/13/100765. If the link does work it may be necessary to zoom out several times and move the map around to find the Geological Garden to the left of the Abbey.